configitems: register the 'web.allowzip' config

mercurial/configitems.py

@@ -724,6 +724,9 b" coreconfigitem('web', 'allowpull',"
 coreconfigitem('web', 'allow_push',
     default=list,
 )
+coreconfigitem('web', 'allowzip',
+    default=None,
+)
 coreconfigitem('web', 'accesslog',
     default='-',
 )